-LRB- CNN -RRB- -- Was it George Zimmerman or Trayvon Martin who screamed for help the night the 17-year-old Martin was shot dead ?

That could depend on which mother the jury believes .

Both Zimmerman 's and Martin 's mothers expressed no hesitation Friday in separate court appearances as to whose panicked voice is heard screaming during a 911 call from that February 26 , 2012 , night in Sanford , Florida : Each said it was her son .

That contradiction -- with Sybrina Fulton insisting it was her son , Trayvon , who cried out , while Gladys Zimmerman said it was her son , George , who was yelling after being attacked by the teen -- was central to Friday 's court proceedings , and central to the second-degree murder case unfolding in central Florida .

Zimmerman has pleaded not guilty and claimed he shot the teenager in self-defense . The 911 call played twice in court on Friday , his lawyers claim , back up their assertion that it was Martin , and not their client , who was the aggressor .

Testifying late Friday afternoon , Gladys Zimmerman said she was sure George was the one yelling . Why ?

`` Because he 's my son . ''

She answered `` all of the above '' when asked whether she had ever before heard her George Zimmerman laugh loudly or cry out for help . This instance , though , Gladys Zimmerman admits was different .

`` I have n't heard him like that before , '' she said as her son wiped away tears in the courtroom . `` The anguish , the way that he is screaming it describes to me anguish , fear , I would say terror . ''

Contrast that to the very different story offered a few hours earlier by Sybrina Fulton , who was stoic as prosecutor Bernie de la Rionda played the 911 call .

When asked whether she recognized the screaming voice , the mother -- who earlier stated that her son was `` in heaven '' -- said it was that of `` Trayvon Benjamin Martin . ''

Trayvon Martin shooting : Fast Facts

Defense attorney Mark O'Mara followed up by asking her , `` As his mother , there was no doubt it was him screaming ? ''

She replied : `` Absolutely . ''

O'Mara then raised the possibility her son , not Zimmerman , was to to blame . `` You certainly hope , as a mom , that your son Trayvon Martin would not have done anything that led to his death , correct ? '' he asked .

`` What I hoped for , '' said Fulton , `` is that nothing happened and he 'd still be here . That 's my hope . ''

Parents ' comments pivotal , or do they cancel each other ?

More than a year ago , the tale of what happened between Trayvon Martin and George Zimmerman captured the nation 's attention and shone a spotlight on gun laws as well as race -- given that Martin is African-American , while Zimmerman is Hispanic .

Moreover , the case prompted some to question Florida 's `` Stand Your Ground '' law , which gives a person facing a `` presumption of fear of death or great bodily harm '' extra protections should they respond with force instead of retreat . Ultimately , Zimmerman chose not to utilize that specific defense .

The trial kicked off nearly two weeks ago with impassioned opening arguments .

The prosecution suggested Zimmerman , whom they painted as a neighborhood watch volunteer who overstepped his bounds , had `` profiled '' Martin because he was black . They called to the stand the 911 dispatcher who told Zimmerman not to follow Martin , though he did anyway . Then there were crime scene and autopsy photos .

And of course , there was the testimony of Rachel Jeantel , who said she 'd been on the phone with her friend Trayvon Martin in the minutes before his death . She testified that she 'd heard Martin call out , `` Why are you following me for ? '' and then say , `` Get off , '' before their call was cut off .

Jeantel has been described as the defense 's star witness . That may still be true . But in many ways , Friday was the most emotional and potentially pivotal day in the trial to date .

O'Mara is n't disputing that latter assertion . He told CNN 's Brooke Baldwin on Friday night that `` once the jury decides who was screaming for help -LRB- on the 911 call -RRB- , if they can , I think everything else falls in line . ''

Speaking to CNN , O'Mara says he does n't dispute that Fulton genuinely believes it was her son 's voice . But so does Gladys Zimmerman of her own son , the defense lawyer says , arguing that `` all the other evidence would suggest '' that the screaming voice is indeed that of George Zimmerman .

And even if not everyone sees it that say , O'Mara opined , it 's possible each woman 's testimony may cancel each other out .

Opinion : Can Zimmerman win over the jurors ?

`` I think the jury is going to look at this and say both of these women just have to live with the belief that it is , in fact , their son , '' O'Mara said . `` And they are going to make a determination not based on what each mom says , but on the other evidence . ''

Daryl Parks , a lawyer for Martin 's family , did n't entirely disagree -- telling CNN that he did n't think the case ultimately `` is going to hinge on whose voice you 're hearing . ''

The six jurors , all women , will weigh both mother 's credibility , others ' testimony and a host of evidence . When all the testimony and presentations are over , Parks said , he expects they 'll agree on a verdict : guilty .

He said , `` At the end of the day , we do not believe that George Zimmerman had to pull out a gun and shoot Trayvon Martin in the heart . ''

Defense challenges medical examiner

Sybrina Fulton and Gladys Zimmerman were n't the only members of their respective families to take the stand Friday .

Jahvaris Fulton , Martin 's older brother , testified Friday morning about the voice on the 911 call . The 22-year-old college student said he was certain that it was his brother , even as he added that he had `` heard him -LRB- Martin -RRB- yell '' before , but `` not like that . ''

Hours later , it was Jorge Meza 's turn . He testified right after Zimmerman 's mother .

A deputy sheriff in Orange County -- which is just south of Sanford , both in central Florida -- he 's also George Zimmerman 's uncle . He said he originally heard the 911 call on TV and without any further information or prompts , immediately recognized his nephew 's voice .

The other highlight of Friday 's court proceedings was the testimony of Voluscia and Seminole County associate medical examiner Shiping Bao .

In Zimmerman 's trial , it 's a jury of millions

Bao said the muzzle of Zimmerman 's gun was likely in loose contact with Martin 's clothing , indicating that the teen was shot at close range .

In testimony that at times turned contentious , Bao also said Martin did not die right away after the gunshot .

`` I believe he was alive for one to 10 minutes after he was shot . His heart was bleeding until there was no blood left , '' the medical examiner said as autopsy photos lingered on a courtroom screen , adding that Martin was `` suffering -LRB- and -RRB- in pain . ''

`` There is no chance he could survive . Zero . ''

During a contentious cross-examination , defense attorney Don West expressed doubts about the condition of Martin 's body and clothing when it was examined , noting the victim was not moved from the scene for about three hours . Bao would not confirm that timeline -- despite West 's repeated attempts to have him do so -- because he said he was not there .

As the two disputed Bao 's ability to establish a timeline , Judge Nelson interjected , telling the witness to `` please stop speaking so Mr. West can ask the next question . ''

Prepared notes that Bao was reading from also drew West 's attention . When asked about them , Bao said , `` I typed out potential answers to your potential questions . ''

Bao objected to sharing his notes , telling the judge that they were private and no one had seen them .

Despite his protests , Nelson allowed the papers to be copied and reviewed by lawyers from both sides .

The notes revealed that Bao had changed his mind about a couple of issues : the amount of time Martin survived after being shot and whether the marijuana in the teenager 's system was enough to affect him .

West argued that the prosecution knew about these changes but did n't tell the defense . But Bao insisted that he did not tell anyone that he 'd changed his opinion .

The defense attorney pressed Bao , too , on the collection of Martin 's clothes and scraping of his fingernails . The medical examiner , though , said he could n't remember each detail and that he 'd trusted that his technicians properly followed procedures .

Late in Friday 's court proceedings , O'Mara made his pitch for acquittal -- arguing that Zimmerman acted in self-defense ; there was no direct evidence of ill will , hatred or spite surrounding Martin 's killing ; and that it was still unclear who could be heard screaming on the 911 call .

There is `` no other reasonable hypothesis '' for what happened , the defense attorney argued , besides self-defense .

The judge , though , denied the motion -- after which , around 5 p.m. , the prosecution formally rested its case .

CNN 's Mariano Castillo and HLN 's Grace Wong contributed to this report .

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NEW : A defense lawyer says other evidence , not the 911 call , will determine the case

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NEW : A lawyer for Martin 's family says he thinks the jury will find Zimmerman guilty

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Gladys Zimmerman says she knows the panicked voice is that of her son

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Earlier , Trayvon Martin 's morther said that it her son 's voice on the 911 call